<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
<style>
    .box{
        width:110px;
        height: 110px;
        border: 5px solid red;
        background-color: saddlebrown;
        border-top: 20px;
        /* 外边距 加auto自动居中 */
        margin: 50px;
    }
    .box1{
        width: 150px;
        height: 150px;
        border: 5px solid black;
        background-color: red;
    }
    .box2{
        width: 100px;
        height: 100px;
        background-color: blue;
    }
</style>
</head>
<body>
    <div class="box">
        <div class="box2"></div>
    </div>
    <div class="box1"></div>
</body>
</html>